1. Field of the Invention
The present invention generally relates to a fiber fixing device for a linear lightguide such as an optical connector, and more particularly, it relates to a fiber fixing device for a linear lightguide which is so improved as to elastically retain an optical fiber.
2. Description of the Background Art
Optical fiber has a function of transmitting information. Referring to FIG. 1, this optical fiber is an innovative medium fundamentally changing the communication system, which has transmitted sounds as electrical signals or electrical conductors for ages. It is not too much to say that the advanced information-oriented society has been started with the appearance of this high technology.
A fiber strand or filament which is made of fused quartz, multicomponent glass or transparent synthetic resin, for example, is employed for a linear lightguide such as optical fiber. The fiber strand or filament, which is extremely thin and breakable in general, is protected by a flexible coating of synthetic resin. In case of forming an optical transmission path with such a linear lightguide, a fiber fixing device such as a connector is mounted on each end portion of the linear lightguide as shown in FIG. 1, for protecting the linear lightguide and locating the optical axis.
In general, various structures that achieve fixing with an adhesive, fixing by mechanical clamping and the like are proposed in relation to the fiber fixing device for a linear lightguide.
FIG. 2 illustrates a fiber fixing device for a linear lightguide employing an adhesive. Referring to FIG. 2, an optical fiber member 102 is formed by a fiber filament 100 and a protective coating 101. This optical fiber member 102 is inserted in a metal fiber guide 103. A clearance between the optical fiber member 102 and the fiber guide 103 is filled up with an adhesive 104. The adhesive 104 is so hardened as to locate and fix the optical fiber member 102 in the fiber guide 103.
FIGS. 3 and 4 are adapted to illustrate a fixing method by mechanical clamping. According to this method, an optical fiber member 102 is inserted in a metal tubular body 105 having a larger diameter, and this tubular body 105 is pressed or crimped by vertically movable parts of a pressing tool 106a and 106b from above and below. Thus, the tubular body 105 retains the optical fiber member 102 with constant force.
Problems of the conventional fiber fixing device for a linear lightguide are now described.
In each of the aforementioned fiber fixing devices, the optical fiber member is directly fixed with an adhesive or a metal tubular body, and hence internal stress is caused in the optical fiber member due to a difference in expansion and contraction resulting from a difference in thermal expansion coefficient between the optical fiber member and the adhesive or the metal tubular body, or due to dimensional dispersion, to disadvantageously hinder the optical characteristics or shorten the life of the optical fiber member.
Further, a fiber fixing device which is tested after fixing a linear lightguide, whereby the assembly is determined to be defective, cannot be disassembled to be reused for re-assembling. Thus, the production yield is uneconomically deteriorated.
In addition, the method of fixing the linear lightguide with an adhesive is inferior in productivity due to the long time required for drying the adhesive.
In the method of directly pressing the optical fiber member, on the other hand, the optical fiber member is disadvantageously stressed or broken if the pressing force is too strong. If the pressing force is too weak, on the other hand, the optical fiber member can slip out of the fiber fixing device after assembling. Thus, the pressing force must be strictly controlled.